Injection molding methods and the injection molding machines required for them are widespread. In order to achieve good utilization of the machines, it is attempted to make vulcanization times as short as possible. The vulcanization time of component parts having a wall thickness of 1 cm is several minutes.
In order to decrease the vulcanization time, an injection molding machine has become known from U.S. Pat. No. 4,370,150, in which a periodically operating heating device is put in between the filling unit and the cross-linking tool, in which a part of the elastomer pressed in by the filling unit is heated to a temperature which just about corresponds to the cross-linking temperature in the cross-linking tool. The cross-linking process is repeated for each injection procedure. Here, a kind of pre-cross-linking of the elastomer takes place, so that the final cross-linking in the cross-linking tool is very much shortened in time. Such a device, however, has the disadvantage that, in the heating zone, cross-linking may occur, which impedes the injection procedure. In the usual injection molding machines for producing elastomer and duromer molded parts, the molding compound in the filling unit is plastified at a temperature that is non-critical to the cross-linking reaction, mostly between 70° and 90° C. Only after injection into the cross-linking tool, which is preheated to the cross-linking temperature, does the cross-linking reaction begin. Cross-linking reaches its maximum speed when the molding compound has reached the cross-linking temperature. Because of the low heat conductivity of the cross-linking molding compounds, the cycle time of the individual injection procedure is essentially determined by the cross-linking time. In this context, the heat transportation from the wall of the tool to the inner part of the molded part, so as to reach a maximum cross-linking speed, is the deciding factor.